The present invention belongs to the field of composite elements manufacturing, in particular obtaining a composite laminate with a high fiber volume.
In composite materials field, a “prepreg” is a unidirectional or oriented arrangement of composite fibers, which are pre-impregnated with an uncured resin, usually partially reacted. The prepreg is as flexible as fibers are, but the fibers cannot move with respect to each other, unless the prepreg is torn, because the resin, despite not being cured, provides an enough strong joint between them.
Prepreg plies are usually stacked one on top of another to form a prepreg laminate. The laminate is then formed and cured to produce the final composite material part. The mechanical properties of the cured part are provided mostly by the fibers in the part. The resin component of the prepreg plies is responsible for providing the necessary tacking during the stacking of the uncured prepreg plies in order to achieve a proper compaction in the laminate. Once a laminate is cured, its porosity must be lower than 2% in order for it to be used in an aeronautic part.
As prepreg plies are made up of fibers impregnated by a resin, if the resin content increases, the fiber content will decrease and vice versa. In most applications, especially aeronautic applications, high mechanical properties are sought. In order to achieve the best mechanical properties possible, the fiber volume must be as high as possible. This, however, means a low resin volume which can be a problem as it will not provide the necessary tacking for a proper compaction of the laminate. This can lead to a higher porosity level than 2% which would result in an unacceptable part for aeronautic purposes. A high porosity level can even cause delamination in the part.
Current manufacturing processes use prepreg plies with a fiber volume lower than 55%, because a higher fiber volume causes a porosity value greater than 2% when curing said pieces, which will lead to delamination.
Document CN103264509 discloses a method of manufacturing a composite element with a fiber volume greater than 60%, but it uses a method of resin injection, which is not compatible with the use of composite prepregs.
The problem to solve is how to achieve an uncured composite laminate with a fiber volume greater than 58% with tacking enough to give rise to a cured composite piece with a porosity value lower than 2%, so that curing this laminate would not lead into delamination due to low tacking level.
Another problem to solve is preventing degradation, which is caused by an excessive heating of the uncured composite laminate before being cured.